Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features is Rare: A Population Based Study of Incidence

The renaming of encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC) to noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was proposed by a group of experts in 2016 to prevent overtreatment of indolent, low-risk thyroid cancers. The aim of this study was to estimate the incidence and outcome for patients meeting the NIFTP criteria in a well-defined geographic region. Our cohort consisted of 134 patients with papillary thyroid carcinoma from the Region of Southern Denmark (RSD), 2007 to 2011. Patients were retrieved from the Danish Thyroid Cancer (DATHYRCA) Database. All potential NIFTP cases were reviewed by a thyroid pathologist. We identified no cases meeting all diagnostic criteria, but one probable NIFTP case from 2007 to 2011. The patient was treated according to the national guidelines and is alive and recurrence-free after 106 months of follow-up. Molecular testing showed KRAS mutation. In a population based set up the incidence rate of NIFTP is very low.

BRAF mutation in cytologically indeterminate thyroid nodules: after reclassification of a variant thyroid carcinoma

Purpose

Fine-needle aspiration biopsy (FNAB) is regarded by the Bethesda system as the gold-standard investigation for stratifying the risk of malignancy of a thyroid nodule. However, some limitations affect the adequacy of the obtained materials, resulting in 30% of the cytological results remaining in the indeterminate category. We aimed to investigate the diagnostic value of the BRAF mutation in cytologically indeterminate thyroid nodules after the reclassification of a variant thyroid carcinoma.

Patients and methods

In this prospective diagnostic study, 76 patients with FNAB findings of atypia of undetermined significance (AUS) and suspicious for malignancy (SUS) were included. The BRAF V600 mutation from FNAB was confirmed by a PCR-based method (Sanger sequencing combined with allele-specific real-time PCR techniques) and immunohistochemistry (IHC). Pathological specimens and features, including noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), were reviewed and compared to the FNAB results.

Results

Using the PCR-based method, the BRAF mutation was positive in 13/76 cases (17.1%), with the diagnostic values of 16.7% sensitivity, 100% specificity, 100% positive predictive value (PPV), and 82.8% negative predictive value (NPV) in the AUS compared to 73.3% sensitivity, 100% specificity, 100% PPV, and 20% NPV in the SUS. For the IHC technique, only 20 of the 76 cytological specimens were qualified for testing. The BRAF mutation was positive in 13/20 cases, with the diagnostic values of 100% sensitivity, 63.6% specificity, 42.9% PPV, and 100% NPV in the AUS compared to 100% sensitivity and PPV in the SUS. The BRAF mutation was not found in the pathological reports for NIFTP.

Conclusion

The malignancy rate is high in our data, with specific and acceptable accuracy rates for the BRAF mutation from FNAB found by using the PCR-based method. NIFTP has been introduced after the pathological reclassification. Molecular diagnosis might be useful to establish the nature of the disease.

Cytomorphology of Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features and the Impact of New Nomenclature on Molecular Testing

The re-naming of noninvasive follicular variant papillary thyroid cancer to the apparently non-malignant, noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) impacts the prevalence of malignancy rates, thereby affecting mutation frequency in papillary thyroid cancer. Preoperative assessment of such nodules could affect management in the future. The original publications following the designation of the new nomenclature have been extensively reviewed. With the adoption of NIFTP terminology, a reduction in the follicular variant of papillary thyroid cancer (FVPTC) prevalence is anticipated, as is a modest reduction of papillary thyroid cancer (PTC) prevalence that would be distributed mainly across indeterminate thyroid nodules. Identifying NIFTP preoperatively remains challenging. RAS mutations are predominant but the presence of BRAF V600E mutation has been observed and could indicate inclusion of the classical PTC. The histological diagnosis of NIFTP to designate low-risk encapsulated follicular variant papillary thyroid cancers (EFVPTCs) would impact malignancy rates, thereby altering the mutation prevalence. The histopathologic criteria have recently been refined with an exclusion of well-formed papillae. The preoperative identification of NIFTP using cytomorphology and gene testing remains challenging.

Cytological features of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)

INTRODUCTION

The noninvasive encapsulated follicular variant of papillary carcinoma (EFVPC) was recently renamed a noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) because of its unique genetic alterations and biological behavior. The objective of this report is to help cytopathologists and cytotechnologists improve diagnostic accuracy and determine the need for cytogenetic studies during adequacy evaluation of thyroid fine-needle aspirations.

MATERIALS AND METHODS

Fifty-five cases of surgery-proven noninvasive EFVPC with corresponding cytology material were reviewed. These cases were collected over 17 years, from 1999 to 2016.

RESULTS

Thirty-four of 55 (61.8%) cases were diagnosed as follicular neoplasm or suspicious for follicular neoplasm on cytology. Eighty to ninety percent of cases showed scant colloid, cellular smears with small clusters of follicular cells with nuclear atypia including enlarged nuclei, oval-shaped nuclei, nuclear grooves, mild chromatin powdering, and rare nuclear pseudo-inclusions.

CONCLUSIONS

NIFTP has unique features: cytologically similar to follicular neoplasms, and nuclear atypia falling between atypia of undetermined significance (category III) and suspicious for/and papillary thyroid carcinoma (category V/VI) (The Bethesda System for Reporting Thyroid Cytopathology).

Updates in Thyroid Cytology

Genomic, clinical, and pathologic studies have prompted a more risk-stratified approach to the management of patients with thyroid nodules. The recent nomenclature change concerning noninvasive follicular thyroid neoplasm with papillary-like nuclear features reflects the clinical trend toward conservative treatment choices for carefully selected low-risk thyroid neoplasms. These developments have occurred in parallel with a growing array of molecular tests intended to improve clinical triage for patients with indeterminate fine needle aspiration diagnoses. This review discusses the implications of the nomenclature revision on the interpretation of thyroid fine needle aspiration and updates available ancillary molecular tests for thyroid fine needle aspirations.

CCND1 Splice Variant as A Novel Diagnostic and Predictive Biomarker for Thyroid Cancer

Cyclin D1 protein is aberrantly overexpressed in thyroid cancers, but mutations of the CCND1 gene are rare in these tumors. We investigated the CCND1 rs9344 (G870A) polymorphism and the expression profiles of wild-type CCND1a and shortened oncogenic isoform CCND1b at the mRNA and protein levels in 286 thyroid tumors. Genotype AA of rs9344 was associated with high expression of CCND1b mRNA and was more frequently found in thyroid cancer than in benign tumors. The mRNA expression levels of CCND1b were higher in papillary thyroid carcinoma (PTC) than in benign or other malignant tumors. However, the expression of CCND1a mRNA showed no association with the parameters. Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was distinguished from PTC by low expression of CCND1b at mRNA and protein levels. We further observed that cyclin D1b immunostaining helped to avoid the misdiagnosis of classic PTC with predominant follicular pattern as NIFTP in a separate cohort. Nuclear cyclin D1b expression was associated with aggressive clinicopathologic features in PTC. These findings suggest that cyclin D1b overexpression can be used as a diagnostic and predictive biomarker in thyroid tumors and may be functionally involved in the development and progression of the disease.

Rare Occurrence of Incidental Finding of Noninvasive Follicular Thyroid Neoplasm With Papillary-Like Nuclear Features in Hürthle Cell Adenoma

INTRODUCTION

Hürthle cell adenoma is a rare benign lesion of the thyroid gland, however, controversies about its potential malignant behavior still remain. Among thyroid neoplasms, papillary carcinoma is the most common variant with great variety of histological subtypes demonstrating different biological behavior.

AIM

To raise the awareness of possible coexistence of these two lesions and discussion about possible therapeutic approaches.

CASE REPORT

A 42 year old female patient was examined because of the pain in the thyroid area. Cytological examination suggested Hürthle cell adenoma. Subsequently, right thyroid lobectomy was performed. Intraoperative frozen sections confirmed the diagnosis, yet final histological analysis revealed encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC), now reclassified as noninvasive follicular thyroid neoplasm with papillary- like nuclear features (NIFTP) within the adenoma, which was not noticed through scintigraphy, ultrasound, cytological and frozen section analysis.

CONCLUSIONS

Problems concerning both diagnostic and therapeutic approach to these lesions are being discussed, since opinions reported in the literature are divided, posing great challenge for the clinician in determining adequate therapeutic procedures.

Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features in Asian Practice: Perspectives for Surgical Pathology and Cytopathology

The introduction of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was initiated and promoted by pathologists. Recent Asian studies added new knowledge to the existing literature to aid a better understanding of NIFTP. Our original data and the results of a meta-analysis suggest that the initial rate of NIFTP has been overestimated, averaging 9.1% (95% confidence interval [CI] 6.0-12.7%) of all papillary thyroid cancers worldwide. The incidence of NIFTP in the Asian population (1.6%, 95% CI 0.9-2.5%; 7 studies) is significantly lower than that reported in the non-Asian series (13.3%, 95% CI 9.0-18.3%; 18 studies). Such difference could be attributed to various perceptions of histological diagnostic thresholds, different nature of papillary thyroid carcinoma, and different approaches in the management of thyroid nodules. The active surveillance for indeterminate nodules and NIFTP, largely represented in the indeterminate cytologic categories, promoted by Japanese institutions establishes a new paradigm to reduce overtreatment of these patients. The lower prevalence of NIFTP in the Asian series indicates a low impact on the risk of malignancy in cytopathology, as it was demonstrated in our original multi-institutional cohort of thyroid nodules, and may predict a low impact on the performance of commercial molecular tests. Several Korean studies addressed the issue of BRAF mutation in NIFTP, which prompted the current refinement of the diagnostic criteria for NIFTP. Our survey of Asian pathologists found that the term NIFTP has not been universally adopted in the local practice. Endocrine pathologists must promote the new entity through provision of educational activities.

The Value of Negative Diagnosis in Thyroid Fine-Needle Aspiration: a Retrospective Study with Histologic Follow-Up

The Bethesda System for reporting thyroid cytopathology (BSRTC) predicts an incidence of malignancy of less than 5% in thyroid nodules with a benign diagnosis on fine-needle aspiration (FNA). However, recent series have suggested that the true rate of malignancy might be significantly higher in this category of patients. We reviewed our experience by performing a retrospective analysis of patients with benign thyroid FNA results who underwent thyroidectomy between 2008 and 2013 at a large academic center. Information including demographics, ultrasound features, FNA diagnosis, and surgical follow-up information were recorded. Slides were reviewed on cytology-histology discrepant cases, and it was determined whether the discrepancy was due to sampling or interpretation error. A total of 802 FNA cases with a benign diagnosis and surgical follow-up were identified. FNA diagnoses included 738 cases of benign goiter and 64 cases of lymphocytic thyroiditis. On subsequent surgical resection, 144 cases were found to be neoplastic, including 117 malignant cases. False negative, defined as interpretation error and inadequate biopsy of the nodule harboring malignancy, was 6%. When cases of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) were excluded from the analysis, false-negative rate was 5%. When microPTC cases were excluded, false-negative rate was 3% and was slightly less than 3% when both microPTC and NIFTP cases were excluded from the analysis. Retrospective review of neoplastic cases showed that 57% were due to sampling error and 43% were due to interpretation error. Interpretation error was more likely to occur in follicular patterned neoplasms (75%), while sampling error was more common in non-follicular variants of papillary thyroid carcinoma (non-FVPTC) (61%). With the exclusion of microPTC, interpretation errors were still more likely to occur in follicular neoplasms (79%) but there was no significant difference in sampling error between non-FVPTC (37%) and follicular patterned neoplasms (42%). Tumor size was larger in cases with interpretation error (mean = 2.3 cm) compared to cases with sampling error (mean = 1.4 cm). This study shows that the false-negative rate of thyroid FNA at our institution is not significantly above the rate suggested by the BSRTC. Interpretation errors were more likely to occur in follicular patterned neoplasms, while non-FVPTC was more frequently found in false negative cases due to inadequate sampling.

A user's guide to non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)

The term non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was recently introduced to replace a subset of follicular variant of papillary thyroid carcinoma (FVPTC). The goal of this change was to promote more conservative management of these tumours and spare patients the psychological burden of a cancer diagnosis. The histological diagnosis of NIFTP is stringent: the tumour needs to demonstrate encapsulation or circumscription, a purely follicular architecture and the presence of nuclear features of papillary thyroid carcinoma, while lacking capsular and vascular invasion, a significant component of solid growth and high-grade features (increased mitotic activity and necrosis). In order to ensure that these inclusion and exclusion criteria are met, the tumour must be sampled extensively, with the entire capsule/periphery submitted in all cases. When sampled by fine-needle aspiration, NIFTP is usually classified within the indeterminate categories of the Bethesda System for Reporting Thyroid Cytopathology. NIFTP is characterized genetically by frequent RAS mutations, although rarely other alterations, such as the BRAF K601E mutation and gene rearrangements in PPARG or THADA, may occur. In this review, we will examine the history of FVPTC and the findings and factors that culminated in the introduction of the NIFTP terminology. A discussion will follow with the histological, cytological and molecular characteristics of NIFTP. We will conclude by considering the potential impact of the introduction of the NIFTP terminology.

Prevalence of BRAFV600E Mutation in Follicular Variant of Papillary Thyroid Carcinoma and Non-Invasive Follicular Tumor with Papillary-Like Nuclear Features (NIFTP) in a BRAFV600E Prevalent Area

BACKGROUND

BRAF^V600E mutation status and prevalence of non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) has not yet been reported in Korea. The aim of this study was to investigate the significance of the BRAF^V600E mutation in the follicular variant of papillary thyroid carcinoma (FVPTC) and to determine the prevalence of NIFTP in BRAF^V600E mutation-prevalent Korean patients.

METHODS

This study retrospectively analyzed 1,417 consecutive patients who underwent total thyroidectomy with routine prophylactic central lymph node dissection for papillary thyroid carcinoma (PTC). BRAF^V600E mutation analysis was performed routinely using multiplex polymerase chain reaction by applying dual priming oligonucleotide. Clinicopathological characteristics and ultrasonographic findings were compared between BRAF^V600E mutation-positive and -negative groups for FVPTC. Pathologists reviewed the pathology slides according to consensus diagnostic criteria for the encapsulated FVPTC and NIFTP.

RESULTS

The prevalence of the BRAF^V600E mutation in all subtypes of PTC was 61.0% (861/1,411). FVPTC presented a BRAF^V600E mutation rate of 27.3%. The FVPTC patients with BRAF^V600E mutation were older than those with no BRAF^V600E mutation (P = 0.021). The prevalence of NIFTP was 0.18% among all PTC patients (2/1,411) and the proportion of NIFTP among FVPTC was 9.1% (2/22).

CONCLUSION

The BRAF^V600E mutation is prevalent in Korean patients with FVPTC in a region with high frequency of the BRAF^V600E mutation and very low prevalence of NIFTP compared with that reported in western studies.

The Bethesda System for Reporting Thyroid Cytopathology Explained for Practitioners: Frequently Asked Questions

BACKGROUND

The recent update of The Bethesda System for Reporting Thyroid Cytology (TBSRTC) is a very important development in the evaluation of thyroid nodules. Clinical experience and scientific literature both show that practitioners performing thyroid fine-needle aspiration are accustomed to basing the clinical management of patients on reports using TBSRTC. Specifically, clinicians are familiar with the percent risk of malignancy corresponding to each TBSRTC diagnostic category (DC), as well as with the respective recommendation for clinical management. However, most clinicians are much less familiar with the specific considerations that lie between a given DC, on the one end, and the respective risk of malignancy and associated management recommendation, on the other end.

SUMMARY

A deeper understanding of the system can enlighten the clinician's thinking about the specific nodule under examination and can guide the decision-making process in a more meaningful way. Such an understanding can only be developed via close two-way communication between cytopathologists and clinicians. Through this type of interaction in the authors' tertiary medical center, recurring issues of particular importance for clinical practice were identified, which are reported here in the form of 16 frequently asked questions posed by the clinician to the cytopathologist.

CONCLUSIONS

For each frequently asked question, an answer is provided based on the literature, the authors' experience, the new version of TBSRTC, and the new World Health Organization classification of tumors of endocrine organs.

Molecular markers in well-differentiated thyroid cancer

PURPOSE

Thyroid nodules are of common occurrence in the general population. About a fourth of these nodules are indeterminate on aspiration cytology placing many a patient at risk of unwanted surgery. The purpose of this review is to discuss various molecular markers described to date and place their role in proper perspective. This review covers the fundamental role of the signaling pathways and genetic changes involved in thyroid carcinogenesis. The current literature on the prognostic significance of these markers is also described.

METHODS

PubMed was used to search relevant articles. The key terms "thyroid nodules", "thyroid cancer papillary", "carcinoma papillary follicular", "carcinoma papillary", "adenocarcinoma follicular" were searched in MeSH, and "molecular markers", "molecular testing", mutation, BRAF, RAS, RET/PTC, PAX 8, miRNA, NIFTP in title and abstract fields. Multiple combinations were done and a group of experts in the subject from the International Head and Neck Scientific Group extracted the relevant articles and formulated the review.

RESULTS

There has been considerable progress in the understanding of thyroid carcinogenesis and the emergence of numerous molecular markers in the recent years with potential to be used in the diagnostic algorithm of these nodules. However, their precise role in routine clinical practice continues to be a contentious issue. Majority of the studies in this context are retrospective and impact of these mutations is not independent of other prognostic factors making the interpretation difficult.

CONCLUSION

The prevalence of these mutations in thyroid nodule is high and it is a continuously evolving field. Clinicians should stay informed as recommendation on the use of these markers is expected to evolve.

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP): impact on the reclassification of thyroid nodules

The 2017 edition of the WHO book on Classification of Tumours of Endocrine Organs includes a new section entitled 'Other encapsulated follicular-patterned thyroid tumours', in which the newly created NIFTP (non-invasive follicular thyroid neoplasm with papillary-like nuclear features) is identified and described in detail. Despite deleting the word 'carcinoma' from its name, NIFTP is not a benign tumor either and is best regarded as a neoplasm with 'very low malignant potential'. The main goal of the introduction of NIFTP category is to prevent overdiagnosis and overtreatment. Sampling constraints, especially when dealing with heterogeneous and/or large nodules, and difficulties in the invasiveness evaluation, are the major weaknesses of the histological characterization of NIFTP. At the cytological level, NIFTP can be separated from classic papillary carcinoma (cPTC) but not from encapsulated, invasive follicular variant PTC. The impact of NIFTP individualization for cytopathology is the drop of rates of malignancy for each Bethesda category in general and for indeterminate categories in particular. The biggest impact will be seen in institutions with a high frequency of FVPTC. The introduction of NIFTP has changed the utility of predictive values of molecular tests because RAS mutations and PAX8-PPARg rearrangements are frequently detected in NIFTP. This turns less promising the application of mutation detection panels as indicators of malignancy and will probably contribute to switch to a rule-out approach of molecular testing. Selection for surgery will go on being determined by a combined detection of clinical, cytological and ultrasound suspicious features.

Ubiquitin Immunostaining in Thyroid Neoplasms Marks True Intranuclear Cytoplasmic Pseudoinclusions and May Help Differentiate Papillary Carcinoma from NIFTP

Papillary thyroid carcinoma (PTC) is defined by an invasive growth pattern and classic nuclear features: enlarged, grooved, overlapping nuclei with chromatin clearing and intranuclear cytoplasmic pseudoinclusions (INCP). True INCPs are characteristic of PTC, but may infrequently be seen in noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP). Nuclear abnormalities that mimic INCP ("pseudo-pseudoinclusions") are common in a variety of thyroid lesions. H&E and ubiquitin-stained whole tissue sections of classic PTC (n = 25) and NIFTP (n = 35) were evaluated. On H&E, true INCPs were present in all (100%) PTCs and absent in all NIFTPs (0%). Pseudo-pseudoinclusions were present in 13 (37%) NIFTPs. In 24 (96%) PTCs, ubiquitin was strongly expressed within INCPs. In NIFTPs, optically clear nuclei or pseudo-pseudoinclusions did not express ubiquitin (0/35). Occasionally, nuclear vacuoles in NIFTP demonstrated a marginated staining pattern, in which strong ubiquitin expression was seen at the periphery of the nucleus, but the central pale area was negative. In addition, 2 NIFTPs demonstrated intrafollicular psammomatoid calcifications which were strongly ubiquitin-positive. Psammoma bodies in PTC were ubiquitin-negative in the majority of cases. We report a previously undescribed finding: strong ubiquitin expression in true INCPs in PTC, absence of true INCPs in NIFTP, and absence of ubiquitin expression in pseudo-pseudoinclusions in NIFTP. This finding supports the difference between true INCPs (found only in PTC) and pseudo-pseudoinclusions (found in NIFTP). Using strict histologic criteria and ubiquitin immunostaining, the presence of true pseudoinclusions may exclude a diagnosis of NIFTP. Caution should be exercised when interpreting nuclear vacuoles or pseudo-pseudoinclusions.

Molecular Testing of Nodules with a Suspicious or Malignant Cytologic Diagnosis in the Setting of Non-Invasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features (NIFTP)

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) is an indolent thyroid tumor characterized by frequent RAS mutations and an absence of the BRAF V600E mutation commonly seen in classical papillary thyroid carcinoma (cPTC). The ability to differentiate potential NIFTP/follicular variant of papillary thyroid carcinoma (FVPTC) from cPTC at the time of fine-needle aspiration (FNA) can facilitate conservative management of NIFTP. The aim of the current study was to investigate how molecular testing may add to cytologic assessment in the pre-operative differentiation of potential NIFTP/FVPTC and cPTC. We had previously evaluated cytologists' ability to prospectively distinguish potential NIFTP/FVPTC from cPTC in a cohort of 56 consecutive FNAs diagnosed as malignant or suspicious for malignancy. We utilized this cohort to perform molecular analysis. Detected molecular abnormalities were stratified into two groups: (1) those supporting malignancy and (2) those supporting a diagnosis of potential NIFTP/FVPTC. The cytologists' characterization of cases and the detected molecular alterations were correlated with the final histologic diagnoses. Molecular testing was performed in 52 (93%) of the 56 cases. For the 37 cases cytologists favored to be cPTC, 31 (84%) had a molecular result that supported malignancy (28 BRAF V600E mutations, 2 NTRK1 fusions, 1 AGK-BRAF fusion). For the 8 cases that were favored to be NIFTP/FVPTC by cytologists, 7 (88%) had a molecular result that supported conservative management (1 NRAS mutation, 6 wild-type result). Seven cases were designated as cytomorphologically indeterminate for NIFTP/FVPTC or cPTC, of which 6 (86%) had a molecular result that would have aided in the pre-operative assessment of potential NIFTP/FVPTC or cPTC/malignancy. These included 3 BRAF V600E mutations in nodules that were cPTC on resection, an HRAS mutation, and a wild-type result in the 2 nodules that were NIFTP, and a TERT promoter mutation along with an NRAS mutation in a poorly differentiated thyroid carcinoma. For nodules with an FNA diagnosis of suspicious for malignancy or malignant, cytologists can differentiate most cases of potential NIFTP/FVPTC from cPTC. However, molecular testing may be valuable for a subset of cases, especially those that are indeterminate for potential NIFTP/FVPTC versus cPTC based on cytologic features alone.

Application of Strict Criteria for Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features and Encapsulated Follicular Variant Papillary Thyroid Carcinoma: a Retrospective Study of 50 Tumors Previously Diagnosed as Follicular Variant PTC

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) was recently proposed as a designation for a subset of follicular variant papillary thyroid carcinoma (FVPTC). Encapsulated FVPTC has been shown to be a fairly indolent tumor, and NIFTP are expected to represent the most indolent subset of these tumors. Many of the exclusion criteria for NIFTP related to architecture and a lack of psammoma bodies are designed to preclude the inclusion of more aggressive non-FVPTC tumors in this indolent group and also exclude the diagnosis of FVPTC. In addition to strict application of histologic features to ensure that NIFTP represents a subset of encapsulated FVPTC without invasion, other exclusion criteria including high mitotic activity and necrosis may also lead to a lack of one-to-one correlation between the diagnosis of NIFTP and encapsulated FVPTC without invasion. In this series, 50 cases previously diagnosed as FVPTC over a 2-year period from a large academic center are retrospectively reviewed for reclassification as NIFTP. Additionally, cases not meeting criteria for NIFTP are more accurately classified using the most up to date WHO criteria. Prior BRAF V600E mutation testing was examined for these tumors when available. Seventeen of 50 (34%) tumors met criteria for classification as NIFTP and, 17 (34%) were classified as encapsulated FVPTC with invasion. Strict application of architectural features led to classification of 12 (24%) tumors as non-FVPTC with a variety of more aggressive designations. Tumors classified as NIFTP and encapsulated FVPTC with invasion lacked lymph node metastases (0/4; 0/7, respectively) and BRAF mutations (0/12; 0/13, respectively). In contrast, infiltrative FVPTC, encapsulated PTC with or without invasion, and conventional PTC showed more aggressive features with lymph node metastases and BRAF V600E mutations. One case not meeting criteria for NIFTP maintained the diagnosis of encapsulated FVPTC without invasion but demonstrated significant mitotic activity (three mitoses/ten HPF) and lacked lymph node metastases and BRAF V600E mutation. These findings demonstrate the importance of using strict criteria, especially the lack of true papillary architecture, for the diagnosis of NIFTP and encapsulated FVPTC to ensure that only truly indolent tumors will be included in these diagnoses and to allow tumors with potential for more aggressive behavior to be appropriately treated.

Preoperative cytologic interpretation of noninvasive follicular thyroid neoplasm with papillary-like nuclear features: a 1-year multi-institutional experience

INTRODUCTION

Encapsulated follicular variant of papillary thyroid carcinoma (PTC) has an indolent behavior; hence, a change in terminology to "noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)" has been proposed. Data are scant on the fine-needle aspiration (FNA) diagnosis of nodules proven to be NIFTP upon resection. The aim was to evaluate the FNA diagnosis of nodules diagnosed as NIFTP upon resection.

MATERIALS AND METHODS

The archives of 8 participating institutions were searched for thyroid resection specimens obtained in a 1-year period, and pertinent demographic and pathology data were recorded.

RESULTS

2226 thyroid surgeries were performed over the indicated time period. NIFTP was diagnosed in 6.3% of cases; 118 patients (119 nodules) with NIFTP and available preoperative thyroid FNA were included. Preoperative cytologic diagnosis were: non-diagnostic: 0.8%; benign: 5.9%; atypia of undetermined significance/follicular lesion of undetermined significance: 42.9%; follicular neoplasm/suspicious for a follicular neoplasm: 31.0%; suspicious for malignancy: 15.9%; malignant: 3.4%. Molecular data was available for 49 cases, either by Afirma or ThyGenX/ThyroSeq. Of the Afirma cases, 11% were classified as "benign", 2% as "indeterminate", and 87% as "suspicious"; of the ThyGenX/ThyroSeq cases, 50% had NRAS mutations, 20% demonstrated KRAS mutations, 20% showed HRAS mutations, and 10% showed a BRAF mutation (K601E).

CONCLUSIONS

NIFTP are tumors demonstrating nuclear features similar to those seen in PTC. Our series shows that a preoperative diagnosis of "suspicious for malignancy" or "malignant" is uncommon in NIFTP, suggesting that there are sufficient cytomorphologic differences between PTC and NIFTP to allow for the suspicion of NIFTP on FNA specimens.

Discriminatory miRNAs for the Management of Papillary Thyroid Carcinoma and Noninvasive Follicular Thyroid Neoplasms with Papillary-Like Nuclear Features

BACKGROUND

Papillary thyroid carcinoma (PTC) variants have several overlapping clinical and pathological features. The World Health Organization recently published a new classification of thyroid tumors containing significant revisions. Encapsulated papillary thyroid carcinoma (EPTC) has been recognized as a distinctive variant of PTC. The noninvasive encapsulated follicular variant of PTC has been reclassified as noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP). Different neoplasms are associated with different outcomes and require different clinical management. The objective of this study was to explore the miRNA expression patterns specific for classic PTC (cPTC), EPTC, follicular variant of PTC, and NIFTP in order to identify biomarkers of diagnostic and prognostic utility aiming for better clinical decisions.

METHODS

The expression of 84 miRNAs was determined by quantitative real-time polymerase chain reaction in 113 thyroid tissues of PTC (classic, encapsulated, and follicular), NIFTP, and hyperplasia lesions. Expression of the same miRNAs was tested in pre- and postoperative whole-blood samples.

RESULTS

Several miRNAs were differentially expressed in the different groups. Expression profile of miRNAs in the tissue was similarly reflected in the circulation. Receiver operating characteristic curve analysis showed that miR-7-5p, miR-222-3p, and miR-146b-5p can discriminate between the different groups with high sensitivity and specificity. Downregulation of miR-144-3p, miR-15a-5p, miR-20a-5p, miR-32-5p miR-142-5p, miR-143-3p, and miR-20b-5p is associated with aggressive behavior in cPTC. Circulating miR-146b-5p, miR-222-3p, miR-155-5p, and miR-378a-3p are potential diagnostic and follow up biomarkers for PTC.

CONCLUSION

Downregulation of miR-7-5p discriminates NIFTP from hyperplasia. Upregulation of miR-222-3p discriminates follicular variant of PTC from NIFTP. High levels of miR-146b-5p distinctively characterize cPTC. These miRNAs are useful biomarkers in the diagnosis of PTC and NIFTP, and help to avoid unnecessary thyroidectomy and improve clinical management.

"Noninvasive Follicular Thyroid Neoplasm With Papillary-Like Nuclear Features" With Focal Spindle Cell Metaplasia

"Noninvasive follicular thyroid neoplasm with papillary-like nuclear features" (NIFTP) is a recent reclassification of the encapsulated follicular variant of papillary thyroid carcinoma, which is supposed to reflect its indolent clinical behavior and to prevent overtreatment of patients with this neoplasm. The diagnosis of NIFTP can only be made histologically on the surgical specimen according to specific inclusion and exclusion criteria, which requires the examination of the whole nodule and its capsule. Spindle cell proliferations, especially of follicular cell origin, arising within thyroid follicular neoplasms are very rare and may cause diagnostic difficulties. Few reports described spindle cell proliferations arising in follicular thyroid adenoma and papillary thyroid carcinoma. To the best of our knowledge, only one case has been reported in NIFTP so far. In this article, we report a unique case of NIFTP associated with a spindle cell proliferation that was characterized immunohistochemically. Specific issues related to this case are discussed.

Does noninvasive follicular thyroid neoplasm with papillary-like nuclear features have distinctive features on sonography?

BACKGROUND

The noninvasive encapsulated follicular variant of papillary carcinoma (nEFVPTC) has recently been reclassified to "noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)," removing this entity from the malignant category. This re-categorization has had major implications for clinical management. NIFTP has overlapping cytohistologic features with papillary thyroid carcinoma (PTC) and with follicular adenomas (FA), but sonographic data comparing NIFTP to PTC and FA is lacking. Our study examines the sonographic features of NIFTP as compared with PTC and FA.

METHODS

Ultrasound scans and Doppler blood flow from subjects who had pre-surgical sonograms and fine needle aspiration biopsies with final surgical pathology diagnoses of NIFTP/nEFVPTC, classical PTC, and FA between 01/2013-08/2016 were assessed. Sonographic and Doppler features as well as Bethesda System (TBS) diagnoses were recorded and analyzed.

RESULTS

40 NIFTP, 58 classical PTC, and 23 FA cases were included. The most common NIFTP pre-surgical TBS cytology diagnosis was Atypia of Undetermined Significance (AUS/FLUS) (40%). NIFTP cases predominantly displayed wider-than-tall shape (100%), smooth borders (75%), occurrence in multinodular glands (82.5%), heterogeneous echogenicity (50%), both perinodular and intranodular Doppler flow patterns (70%), minimal Doppler flow grade (62.5%), and no calcifications (90%).

CONCLUSIONS

Our study demonstrates that NIFTP, PTC, and FA display several distinguishing and overlapping sonographic and Doppler features. Sonographic features appear to complement cytology findings and may help raise pre-operative concern for NIFTP in the proper clinical setting, potentially leading to a more conservative management approach.

Thyroid Nodule Diagnostic Markers in the Face of the New NIFTP Category: Time for a Reset?

BACKGROUND

Current thyroid molecular tests are specifically designed for the differential diagnosis of nodules with indeterminate or suspicious fine-needle aspiration (FNA) cytology.

SUMMARY

However, their clinical validity faces challenges from both variation among institutions in cancer prevalence and, most recently, the new category of non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). The latter diagnosis was previously classified as malignant. Relevant to this, all molecular panels on the market today were originally tested and validated within the context of these entities being considered malignant.

CONCLUSION

This review examines possible effects of the NIFTP reclassification as a precancerous lesion on the original validation studies and, investigates the effect of the significant reported variability in thyroid cancer prevalence on the performance of these tests.

Identification of Two Distinct Molecular Subtypes of Non-Invasive Follicular Neoplasm with Papillary-Like Nuclear Features by Digital RNA Counting

BACKGROUND

The follicular variant (FV) of papillary thyroid cancer (PTC) is one of the most common variants of PTC. Clinically, non-infiltrative FVPTC is considered a low-risk variant of PTC, and the non-invasive encapsulated forms of FVPTC represent a group of thyroid tumors with a particularly good prognosis. Consequently, these neoplasms have been very recently reclassified as non-invasive follicular neoplasms with papillary-like nuclear features (NIFTP). From a molecular standpoint, NIFTP appears to be similar to follicular neoplasms. However, only limited data are currently available regarding their gene expression profile.

METHODS

The aim of this study was to identify specific molecular signatures of 26 NIFTPs compared to those of 19 follicular adenomas (FAs) and 18 infiltrative FVPTCs (IFVPTCs). A nanoString custom assay was used to perform mRNA expression analysis. All cases were also genotyped for BRAF, N-, H-, and K-RAS mutations. Samples were grouped on the basis of gene expression profiles by Pearson's correlation and non-negative matrix factorization clustering analysis. Finally, the uncorrelated shrunken centroid machine-learning algorithm was used to classify the samples.

RESULTS

The results revealed distinct expression profiles of FAs and IFVPTCs. NIFTP samples can exhibit different expression profiles, more similar to FAs (FA-like) or to IFVPTCs (IFVPTC-like), and these different expression profiles largely depend on the presence of different mutations (RAS or BRAF).

CONCLUSION

In conclusion, although further validation of the model is required by using a larger group of prospective cases, these data reinforce the hypothesis that IFVPTC-like NIFTPs might represent precursors of IFVPTC.

Cancer Risk Stratification of Indeterminate Thyroid Nodules: A Cytological Approach

BACKGROUND

Management recommendations for thyroid nodules rely primarily on the cytological diagnosis. However, 25% of biopsies render an indeterminate cytology for which management decision is more challenging due to heterogeneity of the specimens. This study aimed to stratify the cancer risk through subcategorization of indeterminate cytology.

METHODS

The indeterminate cytological specimens (Bethesda-III or IV) of 518 thyroid nodules consecutively evaluated at our academic cancer center between October 2008 and September 2015, blinded to the histological outcome, were retrospectively reviewed. Cytological specimens were subclassified into four groups: aspirates exhibiting nuclear atypia (n = 158; 31%); architectural atypia (n = 222; 43%); oncocytic features (n = 120; 23%); or other types of atypia (n = 18; 3%). The prevalence of malignancy and odds ratio for malignancy were calculated in 323 nodules with histological confirmation.

RESULTS

The prevalence of malignancy was 26% overall (20% in Bethesda-III and 29% in Bethesda-IV; p = 0.07), and 47%, 12%, 24%, and 25% for aspirates with nuclear atypia, architectural atypia, oncocytic features, or other types of atypia, respectively. The OR of nuclear atypia over architectural atypia was 6.4 (3.4-12.2; p < 0.001), and 2.7 over oncocytic features (1.4-5.1; p = 0.01), whereas the OR of architectural atypia over oncocytic features was 0.4 (0.2-0.9; p = 0.03). Results were similar for Bethesda-III and IV aspirates when analyzed independently. Furthermore, cytological subcategories improved cytology-histology correlation, as they were associated with distinct profiles of histological diagnoses (p < 0.001).

CONCLUSIONS

Cytological subcategories can effectively stratify the risk of malignancy of thyroid nodules with indeterminate cytology and improve cytology-histology correlation.

Role of Ultrasound in Predicting Tumor Invasiveness in Follicular Variant of Papillary Thyroid Carcinoma

BACKGROUND

Follicular variant of papillary thyroid carcinoma (FVPTC) is traditionally divided into infiltrative and encapsulated types. Adding to this classification, noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) represents a reclassification of a subset of cases (encapsulated tumors without lymphovascular or capsular invasion). The purpose of this study was to assess the role of ultrasound (US) in predicting tumor invasiveness in FVPTC.

METHODS

From January 2014 to May 2016, preoperative US examinations were performed on 151 patients with 152 FVPTCs who underwent surgery. Based on a pathologic analysis, the FVPTCs were categorized into three groups: NIFTP, invasive encapsulated FVPTC (iE-FVPTC), or infiltrative FVPTC (I-FVPTC). Each nodule was categorized based on the US pattern according to the Korean Thyroid Imaging Reporting and Data System (K-TIRADS) and the American Thyroid Association (ATA) guidelines. The correlation between tumor invasiveness and the K-TIRADS or ATA category was investigated using Spearman's rank correlation coefficient.

RESULTS

Among the 152 FVPTCs, there were 48 (31.6%) NIFTPs, 60 (39.5%) iE-FVPTCs, and 44 (28.9%) I-FVPTCs. US characteristics of the FVPTCs differed significantly according to tumor invasiveness (p ≤ 0.030). Tumor invasiveness showed a significant positive correlation with K-TIRADS (tumors of all sizes: r = 0.591, p < 0.001; tumors ≥1.0 cm: r = 0.427, p < 0.001) and ATA categories (tumors of all sizes: r = 0.532, p < 0.001; tumors ≥1.0 cm: r = 0.466, p < 0.001). According to both K-TIRADS and ATA guidelines for all-sized tumors, the most common subtype was NIFTP in low-suspicion nodules (52.6% and 51.6%), iE-FVPTC in intermediate-suspicion nodules (52.7% and 54.2%), and I-FVPTC in high-suspicion nodules (82.5% and 69.4%). After surgery, lymph node metastases were confirmed in two (4.2%) NIFTP cases, three (5.0%) iE-FVPTC cases, and eight (18.2%) I-FVPTC cases (p = 0.001). The results of the BRAF mutation analysis were not significantly different between the groups (p = 0.507).

CONCLUSIONS

Increasing tumor invasiveness from NIFTP to iE-FVPTC to I-FVPTC is positively correlated with the level of suspicion on US using both K-TIRADS and ATA guidelines.